1. Field of the Invention
The present invention relates to an improvement in an ultrasonic-motor driving apparatus that includes an ultrasonic motor having as a driving source an electromechanical-energy conversion element, such as a layered piezoelectric element, and a driving circuit for the ultrasonic motor.
2. Description of the Related Art
Downsizing of products such as electronic components has been increasingly requested in recent years and reduction in size of motor products, such as an electromotive stage, has been also required. Ultrasonic motors, which provide a larger torque while being smaller than electromagnetic motors, have drawn attention as motors available for downsizing.
Many ultrasonic motors generally utilize frictional force generated in an area where a transducer is in contact with a driven body for driving. With such an ultrasonic motor, the area undergoing friction is intensively worn and, therefore, there are many cases where the ultrasonic motor itself must be replaced with a new one. Hence, ultrasonic-motor driving apparatuses are strongly required in which a new ultrasonic motor can be efficiently driven with higher precision and which do not require a complicated adjustment of a driving circuit, that is, in which the ultrasonic motor is compatible with the driving circuit.
Known technologies pertaining to ultrasonic-motor driving apparatuses include a drive circuit of an ultrasonic motor disclosed in Japanese Unexamined Patent Application Publication No. 6-296378, which is filed by the applicant.
As described in a third embodiment of the specification (pages 5–6) disclosed in the publication, the drive circuit of an ultrasonic motor has a memory for storing values of resonant frequencies specific to an ultrasonic transducer in the ultrasonic motor at its ultrasonic-transducer side (an ultrasonic motor 10 in FIG. 10). The drive circuit of an ultrasonic motor is structured so as to drive the ultrasonic transducer based on the values stored in the memory.
With this structure, even when the ultrasonic motor (a lens 16 in the third embodiment and in FIG. 10) has been replaced in whole with a new one, the ultrasonic motor can be driven in accordance with the resonant frequency of the new ultrasonic transducer.